1. Field of the Invention
The present invention relates to a pneumatic cylinder-and-piston device of the type in which the piston is differentially damped in dependency on its direction of movement within the cylinder, and pertains in particular to improved structure for accomplishing such damping in an efficient, yet simplified and low cost manner.
2. The Prior Art
Differentially damped pneumatic springs are well known, as represented, for example, by U.S. Pat. No. 3,207,498. In this known device, the piston is provided with a piston ring which is axially movable with respect to the piston member between two terminal positions in accordance with the direction of movement of the piston member relative to the cylinder member. In one terminal position, the piston ring functions to open one or more passages across the piston and, in the other terminal position, it functions to close the passage(s). The piston ring thus provides different piston damping rates as a function of the direction of movement of the piston. Although this damping control structure functions satisfactorily, it is relatively expensive from the viewpoints of manufacture and assembly.